The long term objective of this application is to elucidate the roles of pulmonary afferents in cardiopulmonary diseases. Hyperpnea, tachypnea and dyspnea are common symptoms and signs of cardiopulmonary patients. Those patients often hyperventilate, which is detrimental to their existing disease. There are several types of nerve endings in the lung, which provide the respiratory center with information about mechanical and chemical changes. However, what roles these nerve endings play are still not fully understood. Recently, it was discovered that activation of a small fraction of pulmonary receptors by injection of hypertonic saline into the lung periphery doubles neural respiratory activity. This reflex, "excitatory lung reflex," is vagally mediated and is different from all known reflexes evoked from the lungs. After summation by activating more of the receptors, one can imagine the reflex effects being tremendous. Initiation of the reflex may be a key step for the hyperpnea, tachypnea as well as dyspnea during cardiopulmonary diseases. The specific aims of this project are to characterize the excitatory lung reflex and to identify the type(s) of responsible endings. Phrenic nerve activity will be recorded as an index for respiratory drive, intraluminal pressure in the trachea will be recorded as an index for tracheal tone, and activity in the sensory endings will be recorded to quantify the afferent response. Using neurological methodology to stimulate or block nerve traffic, the reflex effects will be assessed and the reflex pathway will be established. The information gained from this project will improve our understanding of neural control of breathing leading to better clinical management of pulmonary problems.